Modulated-oscillator, phonograph transducer



May ll, 1948.v R. B. ALBRIGHT 2,441,464

MODULATED-OSGILLATOR, PHONOGRAPH TRANSDUCER Filed June 15, 1941 3 sheetssheet 1 May l1, 1948. R. B. ALBRIGHT MODULATEDOSCILLATOR, PHONOGRAPH TRANSDUCER s sheets-smet 2 Filed June 13, 1941 [nverzofk- May l1, 1948. R. B. ALBRIGHT 2,441,464

- MODULATED-OSCILLATOR, PHONOGRAPH TRANSDUCER Filed Jane 15, 1941 s sheets-'sheet 3' lVIODULATED-QSCILLATOR, PHONOGRAPH TRANSDUCER Robert B. Albright, Philadelphia, Pa., assighor, by

mesne assignments, to Philco Corporation,` `Philadelphia, Pa., a. corporation of Pennsyl- Vania.

Application June 13, 1941, Serial No. 397,986

7 Claims. (Cl. 179- 100.4)

This invention relates to devices which when l actuated by power in an acoustic system, are capable of supplying power to an electrical system. The invention relates more especially to microphone and phonograph pickup devices and circuits, particularly Where such devices are. `adapted to'vary, by relatively direct means, the

frequency or amplitude, or both, of the output signal of an associated electric Wave generator. The invention is especially adapted for use with phonographs, radio-phonograph combinations, or with small portable radiophone systems and the like.

An important object of the invention is to provide a novel phonograph pickup adapted for use with amplitude modulationy receivers either through the agency of a wireless link or by means of a direct connection.

Another object of the invention is to provide a phonograph pickup device capable of generating a frequency-modulated carrier wave adapted for F. M. (frequency modulation) reception by a standard A. M. (amplitude modulation) receiver.

A further object of the invention is to provide a phonograph pickup device capable of generating a frequency-modulated carrier wave adapted for reception by conventional F. M. receivers.

Still another object of the invention is to provide a novel phonograph pickup device having none of the disadvantageous characteristics of conventional crystalrpickups, particularly with respect to use thereof under damp tropical 'conditions. Y

Another object of the invention is to provide a' novel phonograph pickup device comprising a light-Weight vibratory system together with a vacuum tubeY oscillator circuit for -generating either an amplitude-modulated carrier wave, a frequency-modulated carrier Wave, or both, or an audio frequency output signal corresponding in wave form to the acoustic energy being supplied to the-device.

' A further object of the-invention is to provide a novel microphone and circuit therefor having the characteristics and advantages of the phonographpickup hereinbefore enumerated.

The invention itselfQas Well as other objects thereof, maybe clearly understood by reference to the accompanying drawings, wherein Fig. 1 is aschematic circuit diagram of one embodiment ofV the invention;

Fig. -2 `illustrates a fragmentaryportion of a v modification of the circuit of Fig. 1;

. a radiov receiver ofthe superheterodyne type;

Fig. 5 is an explanatory,y diagram referred to in the description o: the embodiment of Fig. 4; f

Fig. 6 is a plan view of a phonograph pickup constructed in accordance with the principles of the invention;

Fig. '7 is a perspective view of a coil and a molded powdered iron core therefor employed in the pickup of Fig. 6;

Fig. 8 is a perspective view of the coil elements o f Fig. 'Tin operative relation with one form` of vibrating armature;

Fig. 9 is a perspective view of a modified form of the armature of Fig. 8;

Fig. 10 is a planview of an alternative form of pickup turned on its side and with the cover removed; and A Fig. 11 is a sectional view taken on the line I I II of Fig. 10.

Referring now to Fig. 1, there is illustrated one embodiment of the invention by means of which energy in an acoustic (or mechanical) system may be transformed into energy in an electrical system through the agency of a vacuum tube oscillator circuit. The embodiment illustrated includes an oscillator circuit of the tuned-grid tuned-plate type, although it will be understood that other types of oscillator circuits may be employed if desired. The particular oscillator chosen for purposes of illustration includes a tuned grid circuit including the grid inductance I and the grid tuning condenser 2. This tuned grid circuit is coupled to the grid electrode of the .triode 3 by means of a coupling condenser 4. Theanode circuit of the oscillator may comprise an'inductanceS tuned by a condenser 6. Plateto-grid-circut feedback occurs, as is well understood in the art, through the interelectrode capacity between grid and plate. A suitable grid leak 'l may be "connected between the grid and cathode elements of the triode, as illustrated.

Where` the deviceV is to be employed in the reproduction of phonograph records, an armature Y8 and phonograph stylus-holding chuck 9 may be pivoted on the axis I0 in such a manner that vibrations transmitted to the stylus II by the phonograph record will cause the armature 8 to oscillate in a similar manner relative to the inductance coil I, as indicated by the double headed arrow. The armature 8 may comprise, for example, a, single, short-circuited turn, as illustrated in detail in Fig. 10, or it may comprise a thin, relatively stiff leaf of metal foil as shown in Fig. 9. Whatever the specic form of the armature it ispreferred that it be constructed of a light-Weight non-magnetic metallic material, preferably aluminum or an aluminum alloy.

Where a shortcircuited turn is employed. movement of the armature relative to the coil I results primarily in a change in the effective inductance of the coil, changing the resonant frequency of the grid circuit I, 2, and causing the output of the'oscillator to be frequency-modulated in accordance with the faudio frequency components derived from the recording.

Where the armature 8 comprises a thin leaf of metal foil, the relatively high resistance and.

large area of the leaf producesl a condition-where- Y in movement of the armature may have more effect upon the radio frequency resistance of the coil i than upon its inductan'ce. Under these conditions vibration of the-armature will produce corresponding changes in the'Q (ratio of reactance to resistance) of the coil I ,and consequently in the magnitude of` 'the radio fre-- quency voltage thereacross. It follows .that the output of the oscillator .will be amplitude-n'iodu- Vtude modulation is imparted ytothe received signal by the-detuned high frequencycircuits of the receiver. This hybrid signal, having both frequency and amplitude modulation, may then be detected in the usual manner. Y

If the armature 8l associated with'the phonograph pickup is constructed to produce frequency modulation of theR. F. voutput of the oscillator, the radiated signal may be received by a conventional F. M. receiver I3. Where the .frequency deviation produced by the vibrating armature is sufficient the signal may be radiated from the plate inductance directly, or from an antenna attached thereto. However, if the receiver i3 is designed to operate on a signal of band width greater than that which can be supplied directly by the oscillator circuit alone, a suitable frequency multiplier I4 may beradded to increase the deviation ratio of the signal.

'Meansfor accomplishing this 'are well known to those skilled in frequency modulation practices.

As described thus far the desired'audio frequency signal has been secured by amplitude or frequency-modulating a carrier Yfrequency with the kdesired signal, and' by receiving and detecting this modulated 'carrier frequency inV a suitable .radio receiver. This mode of operation is, of course, particularly suitable where it,1 is'desired to operate a phonograph record player at some point remote from .theY receiver, and

kwhere it is desired to eliminate the necessity for ,a wire connection between the phonograph and the radio receiver. There is, however, another way in which the desired Vaudio signal may be derived from the apparatusV and supplied to suitable amplifying equipment. It has been found that `where the vibrating armature 8 is of such construction as to produce substantial changes in the Q of the coil I, there appears lacrossjthe oscillator'grid leak I a pulsating voltage, the audio frequency component ofwhich isY substantially directly proportional to the oscillations imparted to the stylus II by the phonograph record. Accordingly the audio signal present yon thegrid of the oscillator may besupplied directly to a suitable amplifier l5 and loudspeaker IB. By

`way of illustration, the coupling between the A,grid leak 'I and the amplifier I5. is shown to Icoin- Vprise ya switch H, an R. E.ilteri -resistor I8, and

an R. F. filter condenser .119. Y,

The circuits hereinbefore described are not limited in their application to phonograph pick- 1.ups alone.

` For example the circuit may advantageously be adapted to provide a microphone circuit having certain desirable characteristics.

' Thus .the armature and stylus assembly 8-II of Fig. 1 may `be replaced by a diaphragm 20 as is illustrated in Fig. 2. This diaphragm may consist, V'for example, of a strip of 0.0003 duralumin ribbon such as:y is `employed in the construction of ribbon microphones and the like. Under these conditions, the output of the oscillator may be largely amplitude modulated in accordance with the sound waves strikingthe ribbon, in a manner already explained.

A modification ofyethe Amicrophone rcircuit-of Fig. 2.is shown in Fig. 3, wherein 'thereis substituted for lthe'duralurnin ribbon v25J, diaphragm 2i, e.. g. ofthe type-'used in: smallV :loudspeakers, :carrying at' its apex va shortcircuited Y'turn 22 positioned adjacent'theendof vthe oscillator grid -coil I; `1n:this-arrangement.movevment of the short-circuited turn :2-2 relative to the coil-| tends to"frequency-modulatefthe oscillator. output -in ai manner already v'described .with

reference to Fig. 1.

Attentionfis now directed V.to the preferred embodiment of `llig. IIl, in which ithe invention is shown in novel combination-swithfa'radioreceiver of the superheterodynetype, andawherein a common oscillator oircuitiassociated.with-the triode elements of the detectoreoscillator 'tube 23) is employedboth as-the local'oscillatorof the superheterodyne during radio reception, :and as the modulated pickuposcillator during phonograph operation. yThe radio receiveritselffmay comprise a radio frequency `amplifier-2li,-the'detector-oscillator stage-'associated with `the tube 23,

Van intermediate` frequency amplifier 25, second detector and AVC ystage ,25, audio frequency amplifier 2l, and the loudspeaker 28. An automatic volume Vcontrol voltage mayfbe fed Vback tothe high lfrequency amplifier-stages -and'fthe 'first detectorrby Wayrfof theI conductor 29. 'When the switches 30 and 3| arein ytheir left-hand position the ends of the oscillator tank coil `32 are connected, by `Way of the condensers 33 and 34, tothe oscillatorfgrid and vfoscillator anode respectively vof the vacuumv tube 23. 4Inmulti- :band receivers thesWitches SI1-:and 3|y are .preferably a part of the `receivers vband-changing iswitch. A predetermined intermediate tap-point `on v:the coil 32qmay :be `connected -to @ground through a small adjustable 'trimmer' condenser 35, as is Well understood in the far-t. `The "oscillator tuning condenser-,SI5V may vbe connected b-etween the ygrid fend; of the coil :i2-andi` ground, andjmay be ganged Y,witli tuning condenser :3l connected across thersecondary of Vther-l". transformer 38. -A resistorBS--connected between oscillator grid .and cathode -serves asa grid leak, while the resistor.4connected between oscillator anode andB-t-f,V serves -asy the vusualR. F. lter in a shunt feed-.anode supply circuit. yThe intermediate frequency output. of the tube 23-may be supplied to the-I.,.-F..,amplier 2,5-by Y.way of a tuned. transformer. .4 I

When it is `desired to-use. the `receiver .for .the reproduction ofZ phonograph recordatheswitches A3i) and l3! are moved. to their right-,hand position (shown), thereby .i disconnecting the oscillator tank coil. 32 and? its associatedapparatusand substituting therefor, the phonograph, pkllpltank.

minuted iron core 43, as will be explained more fully in connection with the embodiment illustrated in Fig. 6. The coil 42 may be connected to the circuits within the receiver by way of a suitable phonograph pickup cable 44 connected to binding posts P, C, and G, indicating plate, chassis and grid connections respectively. The tank coil 42 may be tuned to resonate at a desired frequency by the addition of a small adjustable shunt tuning condenser 45. When employing the specific form of oscillator circuit shown in Fig. 4 it is generally preferred to design the coil 42 to have fewer turns in its gridto-chassis portion than in its chassis-to-plate portion. By Varying the relative number of turns in these portions the designer will be enabled to control the magnitude of the oscillator voltage which is applied to the pentode Section of tube 23 by virtue of the internal connection of the third grid to the oscillator grid of the triode section of tube 23. In this regard still further latitude of design is allowed through the use of a separate oscillator (e. g. as shown in Fig. l) in connection With a separate first detector or amplier stage.

Where the moving system of the phonograph pickup is adapted largely to vproduce amplitude modulation of the oscillator output, the resonant tank circuit 42, 45, may be adjusted to resonate at the intermediate frequency of the receiver, which may, for example, be of the order of 455 kilocycles. However, if the moving system of the pickup is designed to produce largely a frequencymodulated oscillator output, the circuit 42, 45, is preferably tuned, in the absence of modulation, to resonate at a frequency slightly above or below the intermediate frequency, at a point on the I. F. selectivity characteristic where the said characteristic is substantially linear over an aD- preciable range of frequencies. This is the preferred adjustment.

To illustrate this mode of operation attention is directed to Fig. 5, which illustrates the overall intermediate frequency selectivity characteristic 46 of the I. F. portion of the receiver of Fig. 4. In the illustration the ratio of- Volts output eo to volts input ei is plotted against frequency. This characteristic may be more or less symmetrical about the intermediate frequency, which is here represented by the dashed line v4l and may be, for example, 455 kc. It will be observed that at some intermediate portion of the curve, say in the vicinity of the point 43, the characteristic'is substantially linear over an appreciable range of frequencies. The point 48 may correspond, for eX- ample, to a frequency 5 kc. above the I. F., i. e. to a frequency of 460 kc. The linear portion of the characteristic may extend several kilocycles on either side of the point 48,- as is indicated by the cross-hatched areas below the curve. V

If now the frequency of the oscillator is made to vary about the frequency at 48 and out to limits represented by the solid lines 49 and 50, it will be seen that the radio frequency output eo of the I. F.k amplifier will be caused to vary in amplitude between limits which are proportional to the vertical component of the distance between the intersections of the vlines 49 and 5U with the characteristic 45. Similarly the output voltage of the second detector will be proportional to this same quantity, and consequently the operation of the device will be substantlially linear and the quantity of reproduction satisfactory.

In practice it has been found convenient and desirable to tune the oscillator tank circuit to the point on the curve 46 (Fig. 5) where the slope is maximum, i. e., where the second derivative of the curve is zero. This may be done, for example, by adjusting the trimmer condenser 45 to give maximum audio output while playing a suitable single tone, constant amplitude, test recording.

If the magnitude of the modulated oscillator signal is sufficiently great, it has been found that the AVC voltage rgenerated in the AVC section Y 26 of the receiver maybe sufficiently high to bias thel R. F. amplifier 24 to a point where radio signals are substantially blocked during phonograph operation, making it unnecessary to employ special switching devices for muting the input section of the receiver. Of course, with the local oscillator oscillating at or near the intermediate frequency, in general only those few signals differing from Athe oscillator frequency (or harmonics thereof) by an amount equal to the intermediate frequency could be transferred' through the I. F. amplier in any event.

In one physical embodiment of the above-described apparatus, in which the receivers intermediate frequency Was 455 kilocycles, the tuned circuit 42, 45, Was adjusted to resonate at approximately 460 kilocycles and had an inductance of about 600 microhenries and a capacity of about 200 micromicrofarads. The inductance 42 had 200 turns and was tapped to give about 40 turns and turns in the grid and plate sections of the coil respectively.

The system illustrated in Fig. 4 is of course particularly suitable where the receiver is of the type specifically adapted to receive frequency modulated signals and Where the detector 26 is of the 4so-called discriminator variety. Under these conditions the tuned circuit in the pickup may be adjusted to resonate normally at the center frequency of the intermediate frequency amplifier 25, whence the frequency modulated high frequency signal will be detected in the manner which is conventional for F. M. receivers.

Reference is now made to a physical embodiment of the phonograph pickup, the principal structural features of which are illustratedin Figs.,6, 7, and 8. The pickup may comprise a tone arm 5|, at one end of which means, such as the platform 52, are provided for supportingthe stylus, the armature, and the various electrical circuitelements associated therewith.

The assembly designated generally by referencecharacter 53 provides a pivotal mounting for the stylus and armature. The tone arm structure generally and the mounting 53 are disclosed and claimed in a copending application of Elmer O. Thompson, Serial No. 357,322, filed September 18, 1940, now Patent No. 2,359,808, dated October 10, 1944. These elements are not in themselves a part of the present invention and hence are illustrated only as an example of the environment of the invention.

On the platform 52 there may be mounted an inductance element 54 which is secured to the platform by the clamping means 55. This inductance element may be of the form shown in greater detail in Figs. 7 and 8. In addition to the inductance element there may be provided a small adjustable tuning condenser 56 with which the element 54may be tuned to resonance. The element 54 and the condenser 56 correspond respectively to the coil 42 and condenser 45 of Fig. 4. A terminal strip 51 having soldering lugs 58 may be provided to facilitate making the elec- 'aangaat tricall connections illustrated-in- Eig; 4; As" lillustratedin Figs; "7 and 8 theind-uctancefe'lement may comprise acomminuted iron fcore' and? shell 59 'together with 4a suitable Winding lill The stylus, crank arm, shaft and armature structure and their relation vto the inductance element 59, t5, are best shown in Fig. 8. The movingelements of the pickup comprisel the shaft 61, 'the crank arm 62 andthe stylus 53 Vwhich isriveted in the crank arm as described in the-above- .mentionedapplication of E. O. Thompson. The shaft 6i! is resiliently 4held .in the proper-alignment'by means or the armature .clampand bearing assembly E53. An .upperlrubber ybearing-element Eli and a lower 'rubber bearing-element n'ot shown) provide the necessary resiiience. The lovvei` vbearing element may 'be formed with a square cross section to iit the square bearing portion of the shaft 6i, and tofprovide the necessary restoring Aforce, as described in the above-mentioned rihompson application.

The apertured armature lor vane .'imay kconsist of a modified channelmember 1made from a thin sheet of a suitable light-weight metal. Aluminum foil having a thickness of `05061101 9.095 inch has been found satisfactory for this purpose. The vane should be -rmlyfxed`to the shaft iii so as to rotateor vibrate therewith. The apertured end of the Yvane 65, according `to one yform of the invention, is located near the inductance'element B, 60, and at a point Where the alternating magnetic field Aabout 'theelement is fairly strong. The'eiiect ofthe aperturedvane in this field is similar to that of a single shortcircuited turn of wire, and. consequently the presence or" the vane has an appreciable effect on the eiiective inductance of the coil Gli. 'Moreover, as the vane is vbrated in a fashion to cycli-- callyv `vary its distance from the said coil the inductanc'e ci the coil will, of course, vary cyclically in a similar manner. The operation of the device will be understood from the foregoing description.

.An alternative form of the vane .of Fig. 8 is illustrated in Fig. 9. The channel 'member 65 this instance is not apertured and hence presents a fat unbroken 4surface to the associated inductance element. With this form of vane, vthe chier" eiect produced on the coil Sil by tlie'presence and vibration of the vane isn corresponding variation in the effective resistance of :the coil. This effect is largely produced by the eddy currents set up in the vane by the action of the alternating magneticeld surround'- ingthe coil. As explained in connectionwith-the schematic diagram of Fig. l, either the inductance variation method or the resistance variation method may be used.. 1t shouldfbe understood, however, that in general it will not be possible vready to securepure inductance variation without some resistance variation, or vice versa.-

Inorder to increase the magnetic flux in the immediate vicinity of the vibrating vane, it has sometimes been found convenient to associate with the coil Si? a comminuted iron lcore and shell member S, as illustrated in Fig. *'7. The e-ec't ofsuch a member is to conne the greater part of the fluxto a more or less concentrated path, inwhich the vibrating `vane may be situated, thus greatly increasing the effectiveness ol' the relatively weak vvibrations imparted to the vibrating system by the undulations out in the phonograph record. l

With reference tothepreferred embodiment illustratedin Fig. 4', it should be understood that variations iin? vfthe?-colistantsoit v`theresonant cir- 'ciiitv-Z, E5 v'maybeisecured by varying? the-capacity of 'thercondenser 45 justV asf readily as by "varying the inductance or effective resistance o-- the coil 42.Y Thus chef-movable plate of the condenser 45^ `indicated by the curved arrow) `might be mechanically coupled' to the phonograph stylus' toenable the vibratile plate of the condenser to vibrate'in accordance with the motion of the stylus. '.By way of example, the vibrating. system .of Fig. n9l might be employed without change, the vchannel member Eli' cooper.- ating. with the-stationary plate of condenser 45, Fig. 4, ,totpr'ovide .a condenser whose capacity is `variedin' substantial .accordance with the motion of the.stylustiV Thus,the .pickup of Fig. 6 `utiliz/'zing theI vanefii of Fig. Y9, could be employed with slight .modification to vary the capa'cit'ancez- It' wouldfmerely benecessary to affix a stationary condenser plate rin `the position of element 523, :movngtthe latter to` another position, Aomit condenser 5t, iand1make 'the :necessary electrical .connectionsy Analternative physical embodiment o1" a `pickup adapted/for yuse Withcthis inventioniis illustrated in Figs. 10 and l1. The pickup head .may comrise, for example, a molded case 56 and cover 6l. The case Sfmay be provided'with `a1suitable recess Gl'ato receive aftuning 'condenserzd whose function-corresponds V:toA that of the condenser i5 in Fig. 4. A :cross-:shaped recess .69 having a generally semi-circular vcross-section may also be provided `.to :receive the vibrating elements of the pick-up; 'I'he'covermember'-ltmay be provided Withsimilar andvopposing recesses.

The vibrating member v'Hlmayfcomprise a single aluminum casting having at its upper end a single short-circuitedturn.or'ring 'Ea|,.at its lower end afneedle chuck to'rreceive the needle or stylus 12rat its yright-handuend -a'iirstpivot having a resilient rubber bearingmember 1,3, and at its left-hand end a second pivot :provided with a threaded passage to receive thecooperating needle holding screw 15. This `pivot isalsoxprovided with a rubberbearing member 14. A projecting ytip on the upper end:,of the shorted turn :'H :may be imbedded ina piece of resilientmaterial, such as rubber, toprovide :mechanical damping and 'to permit accurate ,centering roi the armature.

Positioned in a circularV recess in the case Eil and in line With-.the `short-circuitedxturn "il there may be provdedfasuitable coil -'lv corresponding generally'to the coil 42 of Fig. 4, or the coil l An'iron core maybe provided if desired toincreasethe eiiectiveness of small movements of the short-circuited .turn 'il relative thereto as explained vhereinbeore The vibrating vanes 64 and 55 illustrated in Figs..8 'and 9 havesanimportantadvantage over the vibrating member IB of Fig. 10. Because of the relatively large surface which these vanes present to the airthere-'is derived an appreciable degreeof air dampingiwhich acts 'tovdamp out undesired mechanical resonances which otherwise I claim:

1. In an electro-acoustic transducer: an oscillation generator comprising a resonant frequencydetermining circuit, a vacuum tube, and a grid leak connected in the grid circuit of said tube, said generator being adjusted to produce oscillations of high frequency; a vibratile electricallyconductive, loss-inducing element positioned in a portion of the alternating magnetic eld of said resonant circuit and adapted to be vibrated at a low frequency, vibration of said element effecting corresponding variations in the resistance of said resonant circuit, thereby to amplitude modulate the generated high frequency oscillations and to develop a corresponding W frequency signal across said grid leak; and a low frequency output circuit coupled to said grid leak for utilizing the low frequency signal developed thereacross.

2. A phonograph record reproducer comprising: an oscillator having a resonant circuit, a vacuum tube, and a grid leak resistance connected in the grid circuit of said tube, said resonant circuit including an inductance coil and a capacitance, said oscillator being adjusted to oscillate at a radio frequency; a record-engaging stylus; a vibratile metallic vane mechanically coupled to said stylus and electromagnetically coupled to said inductance coil, vibration of said vane by said f stylus at an audio frequency rate effecting corresponding variations in the Q of said coil, thereby to amplitude-modulate the radio frequency oscillation generated by said oscillator, and to develop a corresponding audio frequency signal voltage across said grid leak resistance; means responsive to the audio frequency signal voltage across said grid leak resistance for deriving said signal voltage therefrom; and means for utilizing said derived signal voltage.

3. A phonograph record reproducer comprising: an oscillator having a resonant circuit, a vacuum tube, and a grid leak resistance connected in the grid circuit of said tube, said resonant circuit including an inductance coil and a capacitance, said oscillator being adjusted to oscillate at a radio frequency; a record-engaging stylus; a vibratile metallic vane mechanically coupled to said stylus and electromagnetically coupled to said inductance coil, vibration of said vane by said stylus at an audio frequency rate eecting corresponding variations in the Q of said coil, thereby to amplitude-modulate the radio frequency oscillation generated by said oscillator, and to develop a corresponding audio frequency signal voltage across said grid leak resistance; and means for utilizing said audio frequency voltage.

4. A phonograph record reproducer comprising: an oscillator having a resonant frequencydetermining circuit and a vacuum tube, said resonant circuit including an inductance coil and a capacitance, said oscillator being adjusted to oscillate at a radio frequency; a record-engaging stylus; a vibratile metallic vane mechanically coupled to said stylus and electromagnetically coupled to said inductance coil, vibration of said vane by said stylus at an audio frequency rate effecting corresponding variations in the Q of said coil, thereby to amplitude modulate the radio frequency oscillations generated by said oscillator; and a low-frequency load impedance included in a circuit of said oscillator tube for deriving an audio frequency signal voltage directly from said tube, said voltage corresponding to the amplitude modulation of said radio frequency oscillation.

5. A phonograph record reproducer comprising: an oscillator including a resonant circuit, a vacuum tube, and a grid leak resistance connected in the grid circuit of said tube, said oscillator being adjusted to oscillate at a radio frequency; a record-engaging stylus; means including a vibratile, electrically-conductive, loss-inducing element mechanically coupled to said stylus and electrically associated with said resonant circuit for amplitude-modulating the radio frequency oscillation generated by said oscillator in accordance with audio frequency vibrations of said stylus, and to develop a corresponding audio frequency signal voltage across said grid leak resistance; and means responsive to the voltage across said grid leak resistance for deriving the audio frequency signal voltage therefrom.

6. A phonograph record reproducer comprising: an oscillator including a resonant circuit, a vacuum tube, and a grid leak resistance connected in the grid circuit of said tube, said oscillator being adjusted to oscillate at a radio frequency; record-engaging stylus; means operable by said stylus for amplitude-modulating the radio frequency oscillation generated by said oscillator in accordance with recorded audio frequency vibrations, and to develop a corresponding audio frequency signal voltage across said grid leak resistance; and means responsive to the voltage across said grid leak resistance yfor deriving the audio frequency signal voltage therefrom.

7. A phonograph record reproducer comprising: an oscillator having a resonant frequencydetermining circuit and a vacuum tube, said oscillator being adjusted to oscillate at a radio frequency; apparatus including an impedancevarying phonograph pickup operatively associated with said oscillator for amplitude-modulating-in accordance with recorded audio frequency vibrations-the radio frequency oscillation generated by said oscillator; a resistor includeddn a circuit of said oscillator tube; and means for deriving an audio frequency signal voltage directly from said resistor, said voltage corresponding to the amplitude modulation of said radio frequency. oscillation.

ROBERT B. ALBRIGI-IT.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,548,895 Mertz Aug. 11, 1925 l1,566,634 Trambley Dec. 22, 1925 1,580,510 Little -i. Apr. 13, 1926 1,905,669 Yenzer Apr. 25, 1933 1,915,804 Smith June 27, 1933 1,982,689 Polydoroff Dec. 4, 1934 2,047,817 Bailey July 14, 1936 2,112,010 Brimberg Mar. 22, 1938 FOREIGN PATENTS Number Country Date 373,973 Great Britain Dec. 31, 1932 OTHER REFERENCES Radio Craft Magazine, August 1941, pages 90, 91. 

